Flutable fiber webs with high dust holding capacity

ABSTRACT

The fiber webs described herein may be incorporated into filter media and filter elements. The fiber webs may exhibit a high dust holding capacity. The fiber webs may also exhibit a low thickness. The fiber webs may be sufficiently flexible and/or deformable so that they may be processed to include a series of waves (also known as flutes) that extend along the cross-machine direction.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/339,999, filed Dec. 29, 2011, which is a divisional of U.S.application Ser. No. 12/488,348, filed Jun. 19, 2009, both of which areincorporated herein by reference in their entireties.

FIELD OF INVENTION

The present invention relates generally to filtration and, moreparticularly, to flutable fiber webs that have a high dust holdingcapacity and can be used in filter elements.

BACKGROUND OF INVENTION

Filter elements can be used to remove contamination in a variety ofapplications. Such elements can include a web of fibers. The fiber webprovides a porous structure that permits fluid (e.g., gas, liquid) toflow through the element. Contaminant particles contained within thefluid may be trapped on the fiber web. Depending on the application, thefiber web may be designed to have different performance characteristics.

Fiber webs can be manufactured using conventional equipment. Duringmanufacturing, fibers may be laid down in a continuous process toproduce the web. This can lead to fiber alignment and the fiber webhaving a “machine direction” which is defined by the direction in whichthe web moves along the processing equipment, and a “cross-machinedirection” which is perpendicular to the machine direction. Because ofthe fiber alignment, amongst other effects, properties of the fiber webalong the machine direction can differ from properties along thecross-machine direction.

It may be advantageous to increase the effective surface area of thefiber web in some applications. For example, the fiber web may be wavedto increase surface area. Such waves are generally referred to ascorrugation, if they extend in the machine direction of the fiber web.The waves are called “flutes” if they extend in the cross-machinedirection. The waved fiber webs can be combined with a backing layer toform channels through which fluid may flow. Some filter elementconfigurations can take advantage of the channels and increased surfacearea provided by using fluted webs or by using corrugated webs. Themachine direction and cross-machine direction properties of the web canplay a role in its suitability for use in a particular configuration.

For various applications, it may be beneficial to have filter media withincreased dust holding capacity. In addition, for some applications,filter media may be manufactured to have low thickness. However, inmanufacturing filter media, when maintaining pore size and efficiency, atrade off may exist between having a high dust capacity and a lowthickness of the filter media.

SUMMARY OF INVENTION

Flutable fiber webs that have a high dust holding capacity are describedherein.

In one aspect, a fiber web is provided. The fiber web has a machinedirection and a cross-machine direction. The fiber web includes a seriesof flutes that extend in the cross-machine direction. The fiber web hasa dust holding capacity of greater than about 3 mg/cm² and a thicknessof less than about 30 mils.

In one aspect, a fiber web is provided. The fiber web has a machinedirection tensile elongation of greater than about 2%, a cross-machinedirection tensile elongation of greater than about 2%, a dust holdingcapacity of greater than about 3 mg/cm², and a thickness of less thanabout 30 mils.

In one aspect, a method of manufacturing a fiber web is provided. Themethod includes forming a fiber mixture; forming a resin formulation;non-compressively adding the resin formulation to the fiber mixtureprior to drying the fiber mixture; and drying the fiber mixture with theresin formulation to form a fiber web. The fiber web is capable of beingfluted by including a series of flutes that extend in a cross-machinedirection. The fiber web has a dust holding capacity of greater thanabout 3 mg/cm², and the fiber web has a thickness of less than about 30mils.

In one aspect, a method of filtering a fluid is provided. The methodincludes filtering a fluid using a filter element comprising a fiberweb. The fiber web includes a series of flutes that extend in thecross-machine direction. The fiber web has a dust holding capacity ofgreater than about 3 mg/cm² and a thickness of less than about 30 mils.

Other aspects, embodiments, advantages and features of the inventionwill become apparent from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In thedrawings, each identical or nearly identical component that isillustrated in various figures is represented by a like numeral. Forpurposes of clarity, not every component may be labeled in everydrawing. In the drawings:

FIG. 1 depicts a fiber web with flutes that extend in the cross-machinedirection in accordance with some embodiments;

FIG. 2 depicts a coating process for coating a web of fibers with aresin in accordance with some embodiments;

FIG. 3 depicts a fluted fiber web that is laminated to a backing andwrapped into a spiral in accordance with some embodiments;

FIG. 4 depicts a graph of Palas filtration performance for two examplesof a fiber web showing variations of the mass of dust accumulated andpressure drop in accordance with some embodiments.

DETAILED DESCRIPTION

The fiber webs described herein may be incorporated into filter mediaand filter elements. The fiber webs may exhibit a high dust holdingcapacity. In addition, the fiber webs may exhibit a low thickness. Thefiber webs may be formed by coating a mixture of wet laid fibers with aresin using a generally non-compressive coating process (e.g., curtaincoating). The webs may also be sufficiently flexible and/or deformableso that they may be processed to include a series of waves (also knownas flutes) that extend along the cross-machine direction of the webswithout visibly cracking or splitting the webs. The flutes increase theeffective surface area of the webs which can enhance filter performance.The flutes also provide web surface separation which can form channelswithin the resulting filter elements, through which fluid may flow. Forexample, channels may be formed between a fluted fiber web and a backingapplied to the web. As described further below, the fiber webs caninclude various components (e.g., different fiber types, resin) whichare selected and combined according to a suitable process to impart thedesired high dust holding capacity, low thickness, and mechanicalproperties. The webs may be incorporated into a variety of types offilter elements which are used in a number of applications including, inparticular, those that benefit from an increased dust holding capacity.

The fiber webs may be formed of one or more types of fibers and a resinformulation to provide mechanical and chemical properties. As describedfurther below, a resin formulation may comprise several componentsincluding a resin, a crosslinking agent, and other additives. However,in some embodiments, additives may be provided to the fiber webseparately from the resin formulation.

In some cases, fiber(s) may be the principal component of the fiber web.That is, in these cases, the total fiber weight percentage may begreater than the weight percentage of any other component in the web.For example, the fiber component(s) may comprise between about 50% andabout 95% of the total weight of the fiber web. In some embodiments, thefibers make up between about 55% and about 90% (e.g., between about 60%and about 85%) by weight of the fiber web. The resin formulation maycomprise the remainder of the fiber web that is not the fibercomponent(s) in certain embodiments. In some embodiments, the resinformulation comprises between about 1% and about 50% of the total weightof the fiber web. In some embodiments, the resin formulation includesbetween about 5% and about 45% (e.g., between about 20% and about 40%)by weight of the fiber web.

It should be understood that in some embodiments the fiber web mayinclude fiber component(s) and/or resin formulations outside theabove-noted ranges.

In general, the fiber component(s) of the fiber web may be formed of anysuitable composition. Suitable compositions include cellulose, syntheticmaterials, and glass. As described further below, it may be preferableto use cellulose fibers as a single fiber composition in the fiber web;though, in other cases, a blend of different fiber compositions may beused.

Suitable cellulose fiber compositions include softwood fibers, hardwoodfibers and combinations thereof. Examples of softwood cellulose fibersinclude fibers that are derived from the wood of pine, cedar, alpinefir, douglas fir, and spruce trees. Examples of hardwood cellulosefibers include fibers derived from the wood of eucalyptus (e.g.,Grandis), maple, birch, and other deciduous trees.

Suitable synthetic fibers include fibers formed from polyaramid,polypropylene, polyethylene, polyamide, polyether ether ketone,polyester (e.g., PET), lyocell, rayon, and combinations thereof. Itshould be understood that other types of synthetic fibers may also beused. Various synthetic fiber configurations may also be used. In someembodiments, synthetic fibers may have a single composition; or, inother embodiments, synthetic fibers may have multiple compositions. Thatis, an individual synthetic fiber may have a single composition in someembodiments; or, in other embodiments, an individual synthetic fiber mayhave multiple compositions. When the fibers have multiple compositions,the fibers may be referred to as multi-component fibers. An example of amulti-component fiber is a bi-component fiber which includes a firstmaterial and a second material. Multi-component fibers may have avariety of spatial arrangements of their components including acore-sheath configuration (e.g., the first material may be a sheathmaterial that surrounds the second material which is a core material), aside by side configuration, a segmented pie arrangement, a tri-lobalarrangement (e.g., the first material may be at the tip of the lobe) andan arrangement of localized regions of one component in the othercomponent (e.g., “islands in sea”).

Suitable glass fibers may include chopped strand glass fibers ormicroglass fibers.

As noted above, the fiber web may include a primary fiber type. In someof these embodiments, the cellulose fibers may be the primary fibertype. In some embodiments, all of the fiber in the web may be cellulosefiber. In some embodiments, the fiber web may include between about 50and about 95 weight percent cellulose fibers. In some embodiments, thefiber web may include between about 55 and about 90 weight percent(e.g., between 60 and 85 weight percent) cellulose fibers. In some ofthese embodiments, the cellulose fiber within the web may comprise bothsoftwood and hardwood fibers. For example, the fiber web may includebetween about 0 and about 95 weight percent (e.g., between 30 and 60weight percent, or between 35 and 50 weight percent) softwood andbetween about 0 and about 95 weight percent (e.g., between 20 and 40weight percent, or between 25 and 35 weight percent) hardwood. It shouldbe understood that some embodiments may include fiber compositions andweight percentages outside the above-noted ranges. In some cases,cellulose fibers may naturally absorb water to a certain percentage(e.g., 3-5% of the fiber weight).

In general, cellulose fibers may have any suitable dimensions. In someembodiments, the average diameter of the cellulose fibers are less thanabout 50 microns. For example, the average fiber diameter may be betweenabout 5 microns and about 50 microns. The general dimensions of softwoodand hardwood cellulose fibers may vary depending on the type of treethat the cellulose fibers are derived from. The diameter of softwoodcellulose fibers may generally be less than about 50 microns, betweenabout 10 microns and about 40 microns, or between about 20 microns andabout 30 microns. The aspect ratio of softwood cellulose may rangebetween about 10 and about 300, between about 20 and about 200, orbetween about 30 and about 50. The diameter of hardwood cellulose fibersmay generally be less than about 50 microns, between about 5 microns andabout 50 microns, or between about 10 microns and about 20 microns. Insome embodiments, the aspect ratio of hardwood cellulose may rangebetween about 10 and about 300, between about 20 and about 200, orbetween about 30 and about 60.

The fiber web may include more than one type of fiber, for example, ablend of cellulose fibers and synthetic fibers. In some cases, theweight percentage of cellulose fiber may be greater than the weightpercentage of synthetic fiber. In other cases, the weight percentage ofsynthetic fiber may be greater than the weight percentage of cellulosefiber. In some embodiments, the principal fiber type may be syntheticfibers, e.g., between about 50% and about 95%, between about 55% andabout 90%, between about 60% and about 85% of the total weight of thefiber web may be synthetic fibers. In some embodiments, all of the fiberin the web may be synthetic.

In addition to the fiber component(s), the fiber web includes anappropriate resin formulation. As noted above, the resin formulation caninclude a number of different components such as a resin, and acrosslinking agent, amongst other additives. In some embodiments, theresin formulation may be between about 1% and about 50%, between about5% and about 45%, or between about 20% and about 40% of the total weightof the fiber web.

The resin is generally the principal component of the resin formulation.That is, the resin is generally the largest component by weight of theresin formulation. In some cases, the resin may be between about 1% andabout 50%, between about 5% and about 45%, or between about 20% andabout 40% weight of the fiber web.

In general, any suitable resin may be used. Examples of suitable resinsinclude polymers such as styrene acrylic, acrylic, polyethylene vinylchloride, styrene butadiene rubber, polystyrene acrylate, polyacrylates,polyethylene vinyl chloride, polyvinyl chloride, polynitriles, polyvinylacetate, polyvinyl alcohol derivatives, starch polymers, epoxy,phenolics, and combinations thereof, including both waterborne andsolvent versions. It should be understood that other resin compositionsmay also be suitable. In some embodiments, the resin may exhibit a glasstransition temperature less than about 60° C., between about 10° C. andabout 55° C., or between about 20° C. and about 40° C. In some cases,the resin may be in a latex form, such as a water-based emulsion.

The resin may exhibit self-crosslinking or non-crosslinking behavior.For example, a self-crosslinking resin may include monomers (e.g.,N-methylolacrylamide, or other crosslinking groups) in the backbone thatexhibit crosslinking behavior. If the resin material is notself-crosslinking, then an appropriate crosslinking agent may be addedto the resin material. The weight percentage of the crosslinking agentbased on the total weight of the resin formulation (when dry) can beless than about 20 weight percent, between about 1 and about 10 weightpercent, and, in some cases, between about 0.5 and about 2.5 weightpercent. The fiber web may include less than about 1 weight percent ofthe crosslinking agent. Examples of suitable crosslinking agents includemelamine formaldehyde, alkylated melamine formaldehyde, N-alkylmelamine, DMDHEU, epoxy, aziridine, and/or combinations thereof.

It should be appreciated that other crosslinking agents and/or weightpercentages may also be suitable.

The fiber webs may also include other conventional additives that may beadded to impart desirable characteristics. For example, to impartantimicrobial and/or antifungal properties, the webs may includesuitable antimicrobial and/or antifungal agents such as silver orsilver-based compounds, copper or copper-based compounds,diiodomethyl-p-tolysolfone, methyl peracept,5-chloro-2-(2,4-dichlorophenoxy) phenol, triclosan, pyrithion derivates,halogenated phenoxy compounds, and zinc 2-pyridinethiol-1-oxide, amongstothers. In some embodiments, the fiber web may include a flame retardantagent such as antimony trioxide, decabromodiphenyl ether, halogenatedpolymers, halogenated compounds, phosphorous-based compounds (e.g.,diammonium phosphate), aluminum-based compounds, nitrogen-basedcompounds, magnesium sulfate, and guanidine, amongst others. In someembodiments, the fiber web may include a conductive material such asgraphite, carbon black, metals (e.g., aluminum, iron, copper),conductive polymers and/or resins (e.g., derivatives of polyacetylene,polyaniline, Polypyrrole, Poly(phenylene vinylene),poly(3-alkylthiophenes), amongst others), doped materials (e.g.,phosphorus-doped, boron-doped), and conductive salts, amongst others.

As noted above, additives may be present as a separate component fromthe resin formulation in some embodiments.

The fiber webs may be incorporated into a filter media. The filter mediamay include a single fiber web or more than one fiber web havingdifferent characteristics. The filter media may also include othercomponents in addition to the fiber web(s), such as a backing, alaminated scrim, and/or additional additives as described above.

As noted above, the fiber webs described herein can include a series offlutes. The flutes, for example, may be in the form of a sinusoidalpattern of waves. In certain preferred embodiments, the flutes extend inthe cross-machine direction as shown in FIG. 1. As shown, fiber web 10has a machine direction 20 and a cross-machine direction 22. The fiberweb 10 has flutes 12 having peaks and valleys where the flutes runparallel to the cross-machine direction 22. As noted above, thecross-machine direction 22 is perpendicular to the machine direction 20and the machine direction 20 is defined by the direction in which thefiber web moves along the processing equipment. However, it should beunderstood that not all embodiments are limited to flutes that extend inthe cross-machine direction. When a fiber web is considered to beflutable, the fiber web may undergo a fluting process such that novisible cracking or splitting of the fiber web occurs.

The flutes of the fiber web may be within a range of frequencies andamplitudes. For example, the frequency of flutes may be greater thanabout 1 flute/inch, between about 1 flute/inch and about 20 flutes/inch,or between about 4 flutes/inch and about 8 flutes/inch. The amplitude ofthe flutes may range between about 1 mil and about 100 mils, betweenabout 5 mils and about 75 mils, or between about 10 mils and about 45mils. As used herein, the amplitude is defined as the distance betweenthe top of a peak and bottom of a valley. In general, in a given fiberweb, the flutes generally have a similar amplitude and similar frequencyacross the web, though that is not a requirement. It should also beunderstood that flute frequencies and amplitudes outside the above-notedranges are possible.

In some embodiments, it may be preferable for the fiber web to besufficiently flexible and/or deformable to facilitate formation of thefluted structure described above. The flexibility and deformability canbe characterized by a number of mechanical properties including Mullenburst tests and tensile tests.

In general, the Mullen burst tests measure the pressure required forpuncturing a fiber web as an indicator of the load carrying capacity ofthe fiber web under specified conditions. Mullen burst may be measuredfor the fiber web in both dry and wet conditions. In some embodiments,the dry Mullen burst for the fiber web may be greater than about 15 psi,between 15 psi and about 90 psi, or between about 20 psi and about 60psi. Additionally, the as is (prior to cure) wet Mullen burst may bebetween about 5 psi and 80 psi, between about 7 psi and about 50 psi, orbetween about 10 psi and about 35 psi. The fully cured wet Mullen burstmay be between about 10 psi and 100 psi, between about 15 psi and about70 psi, or between about 20 psi and about 40 psi. The ratio of the as iswet Mullen tests to the fully cured Mullen tests may be between about0.1 and about 1.0, between about 0.3 and about 0.95, or between about0.7 and about 0.9. Mullen burst tests are measured following theTechnical Association of the Pulp and Paper Industry (TAPPI) Standard T403 om-91, “Bursting strength of paper.”

The fiber web may have different tensile properties in the machinedirection as compared to the cross-machine direction. In someembodiments, the tensile elongation values in the machine direction maybe less than that in the cross-machine direction, while the tensilestrength values in the machine direction may be greater than that in thecross-machine direction. For example, the machine direction tensileelongation of the fiber web may be greater than about 2%, between about2% and about 8%, or between about 3% and about 5%. The cross-machinedirection tensile elongation of the fiber web may be greater than about2%, between about 2% and about 15%, or between about 4% and about 10%.The machine direction tensile strength of the fiber web may be greaterthan about 10 lb/in (e.g., between about 10 lb/in and 50 lb/in, orbetween about 20 lb/in and 30 lb/in). The cross-machine directiontensile strength of the fiber web may be greater than about 3 lb/in(e.g., between about 7 lb/in and about 30 lb/in, or between about 10lb/in and about 20 lb/in). In some cases, the cross machine directiontensile strength may be greater or less than the machine directiontensile strength. The ratio between the machine direction tensilestrength and cross machine direction tensile strength may range betweenabout 0.5 and about 5, between about 1 and about 4, or between about 1.5and about 2.5. Tensile tests are measured following TAPPI Standard T 494om-88, “Tensile breaking properties of paper and paperboard (usingconstant rate of elongation apparatus)” using a pull rate of 2″/min.

In some embodiments, the machine direction wet Gurley stiffness of thefiber web may be measured to be greater than about 10 mg, between about10 mg and about 2000 mg, or between about 50 mg and about 500 mg. Insome embodiments, the machine direction dry Gurley stiffness of thefiber web may be measured to be greater than about 200 mg, between about200 mg and about 3000 mg, or between about 400 mg and about 1200 mg.Gurley stiffness tests are measured following TAPPI Standard test 543,“Bending stiffness of paper.”

In general, the fiber web may have any suitable basis weight. Forexample, the basis weight of the fiber web may range from between about20 g/m² and about 150 g/m², between about 60 g/m²and about 80 g/m², orbetween about 30 g/m²and about 100 g/m². The basis weight of the fiberweb is measured according to TAPPI Standard T 410 om-93.

In general, the fiber web may have any suitable thickness. Suitablethicknesses include, but are not limited to, less than about 30 mils,between about 2 mils and about 25 mils, or between about 5 mils andabout 15 mils. The fiber web thickness is determined according to TAPPIT 411 om-89, “Thickness (caliper) of paper, paperboard, and combinedboard” using an electronic caliper microgauge 3.3 Model 200-Amanufactured by Emveco, www.emveco.com, and tested at 1.5 psi.

The fiber web may have a range of permeability. For example, thepermeability of the fiber web may range from between about 5 cubic feetper minute per square foot (cfm/sf) and about 200 cfm/sf, between about5 cfm/sf and about 100 cfm/sf, between about 10 cfm/sf and about 80cfm/sf, or between about 15 cfm/sf and about 50 cfm/sf. The permeabilityof the fiber web is measured according to TAPPI Method T251. Thepermeability of a fiber web is an inverse function of flow resistanceand can be measured with a Frazier Permeability Tester. The FrazierPermeability Tester measures the volume of air per unit of time thatpasses through a unit area of sample at a fixed differential pressureacross the sample. Permeability may be expressed in cubic feet perminute per square foot at a 0.5 inch water differential.

In some embodiments, the PMI mean flow pore size of the fiber web maybe, for example, greater than about 5 microns, between about 5 micronsand about 50 microns, or between about 10 microns and about 20 microns.Mean flow pore size is measured using ASTM Standard F 316, “Pore sizecharacteristics of membrane filters by bubble point.”

The fiber web can also be characterized by Palas filtration performance.Such testing is based on the following parameters: test filter area ofthe fiber web is 100.0 cm²;

face velocity is 20.0 cm/sec; dust mass concentration is 200.0 mg/m³;dust/aerosol is SAE fine; total volume flow is about 120.0 L/min, and nodischarge. Palas filtration performance is generally measured accordingto ISO Procedure 5011:2000, “Inlet air cleaning equipment for internalcombustion engines and compressors—performance testing.”

Palas filtration testing is used to measure the dust holding capacity.The dust holding capacity is the difference in the weight of the fiberweb before the exposure to the fine dust and the weight of the fiber webafter the exposure to the fine dust when the pressure drop across thefiber web reaches 1,500 Pa, divided by the area of the fiber web. Dustholding capacity may be determined according to the weight (mg) of dustcaptured per square cm of the media (e.g., through a 100 cm² test area).In some embodiments, the dust holding capacity may be greater than about2 mg/cm², greater than about 3 mg/cm², greater than about 3.5 mg/cm²,between about 2 mg/cm² and about 8 mg/cm², between about 3 mg/cm² andabout 8 mg/cm², between about 3 mg/cm² and about 5 mg/cm², or betweenabout 3.5 mg/cm² and about 5 mg/cm².

The initial fractional efficiency may be characterized using Palasfiltration tests. In some embodiments, the initial fractional efficiencyof the fiber web for particles approximately 0.3 microns in size may begreater than about 50%, between about 50% and about 99%, or betweenabout 60% and about 90%. In some embodiments, the initial fractionalefficiency (efficiency at a given particle size) of the fiber web forparticles approximately 1.0 micron in size may be greater than about80%, between about 80% and about 99.99%, or between about 90% and about99.99%. It can be appreciated that the larger the particle size, themore likely the particles will be captured.

The initial dust retention may also be characterized using Palasfiltration tests. In some embodiments, the initial dust retention(efficiency for all particles in the dust) of the fiber web may begreater than about 60%, between about 70% and about 100%, or betweenabout 80% and about 100%.

The initial pressure drop may also be characterized using Palasfiltration tests. In some embodiments, the initial pressure drop may beless than 500 Pa, between about 80 Pa and about 300 Pa, between about99.99 Pa and about 300 Pa, between about 200 Pa and about 300 Pa,between about 80 Pa and about 200 Pa, or between about 80 Pa and about99.9 Pa.

It should be understood that, in some embodiments, the fiber web mayhave property values outside one or more of the above-noted ranges.

In general, the fiber web may be processed using conventional techniquesand equipment. For example, in some embodiments, a wet laid process maybe used to form the fiber web. Suitable techniques can involve formingthe resin formulation and a fiber mixture in separate processes,followed by a suitable step (e.g., coating or impregnation) whichcombines the two. The specific process depends, in part, on theparticular components being used. Those of ordinary skill in the artknow suitable parameters and equipment for such processing. Thefollowing paragraphs include an exemplary description of a processsuitable for producing a fiber web that includes cellulose fibercomponents.

The fiber web formation process can involve mixing softwood and hardwoodcellulose fibers together to form a fiber mixture comprising a pulpedfiber blend. In some embodiments, the cellulose fibers are added to apulper with water and stirred until the fibers are suitably dispersed.Additional water is then added to the fiber dispersion for dilution to adesired consistency (e.g., the fiber content is about 0.01% to about 6%of the total fiber/water dispersion). In some embodiments, cellulosefibers may be blended with other fibers (e.g., synthetic fibers such aspolyester). For example, other fibers may be added to the dispersion ofcellulose fibers followed by additional dilution with water to reach thedesired consistency (e.g., the fiber content is about 0.01% to about 6%of the total fiber/water dispersion).

The dispersion of fibers are continually mixed and then subsequentlyformed into a fiber web using a suitable sheet forming equipment such asa delta former, an inclined wire, a fourdrinier, or a rotoformer.

As noted above, the resin formulation can be prepared in a separateprocess from the fiber web. For example, the components of the resinformulation including the resin, the crosslinking agent (if present),and additives are mixed in a mixer and diluted with water to anappropriate solids level (e.g., between about 1% and about 50% solids,or between about 5% and about 15% solids). Solids level is defined asthe percentage of solids in a liquid media whether in a solution or adispersion. In general, the mixture should be relatively uniform andcontinuous. In some cases, as noted above, additives may be added to thefiber web separate from the resin formulation.

Upon suitable mixing of the fiber component(s), a portion of the resinformulation mixture may be applied to the fiber web using anon-compressive coating technique. The non-compressive coating techniquemay coat the fiber web, while not substantially decreasing the thicknessof the web. In some embodiments, a curtain coater is used fornon-compressively coating the fiber web with the resin formulation. FIG.2 illustrates an embodiment of a curtain coating process. As shown, wetlaid fiber component(s) 10 a are drawn along a conveyor 60 (in adirection depicted by the dashed arrow) toward a resin coater 70 and avacuum 80. The resin coater 70 includes the resin formulation 72 which,through gravity, is applied as a stream to the wet laid fibers on theconveyor 60. At the same time, the vacuum 80 pulls the resin formulation72 toward the conveyor 60 through the wet fiber component(s), formingresin coated fiber component(s) 10 b. In some cases, in addition topulling the resin formulation through the fibers, the vacuum may alsoexert sufficient pulling pressure to pull the actual fiber component(s)toward the conveyor, decreasing the overall thickness of the fibercomponent(s). In addition, various coating conditions such as the linespeed (e.g., speed at which the conveyor moves relative to the fibercomponent(s)) and the strength of the vacuum may influence the residualamount of resin content in the fiber web.

It should be understood that the process and configuration shown in FIG.2 may have a variety of modifications.

It can be understood that other generally non-compressive techniques maybe used to apply the resin formulation to the wet laid fibercomponent(s) in forming the fiber web. For example, techniques that maybe used for non-compressively adding resin formulation to the wet laidfiber component(s) include, but are not limited to, gap sized presscoating, spray coating, slot application, foam application, anddoctor/knife coating, amongst others. For instance, in gap sized presscoating, a gap is provided between rotating cylinders of a gravure pressso that compression of the fiber web is limited. Foam coating involves asimilar process to that shown in FIG. 2 for curtain coating exceptinstead of the stream of resin formulation provided to the fibercomponent(s) having a specific gravity of generally greater than orequal to 1 g/ml (e.g., for curtain coating), the stream of foam that isprovided to the fiber component(s) has a specific gravity of generallyless than 1 g/ml. In foam coating, the stream of resin formulationincludes entrapped gas.

In some embodiments, a portion of the resin formulation may be added tothe fiber component(s) in a wet phase and a portion of the resinformulation may be added to the fiber component(s) after drying. Forexample, a portion of the resin formulation of the fiber web is appliedto the wet laid fiber component(s) prior to drying using anon-compressive coating technique (e.g., curtain coating), the portionbeing approximately between about 1 and about 99, between about 10 andabout 80, or between about 30 and about 60 percent weight of the entireresin formulation of the fiber web. Another portion, or the remainder,of the resin formulation of the fiber web may be applied after drying ofthe fiber web.

In some embodiments, the entire resin formulation of the fiber web isapplied to the wet laid fiber component(s) prior to drying using agenerally non-compressive coating technique to form the fiber web.

The fiber web is dried using appropriate methods which may utilizeultrasonic or microwave techniques, steam cans, infrared heaters (gasand/or electric), or air ovens. Typical drying times may be betweenabout 5 seconds and about 10 minutes (e.g., about 5 minutes) and dryingtemperatures may range between about 100° F. and about 500° F. (e.g.,about 300° F.).

As mentioned above, another portion or the remainder of the resinformulation mixture of the fiber web may then be added to the driedfiber web. For example, the resin formulation mixture may be provided asa coating on the fiber web. In some embodiments, a further portion ofthe resin formulation added to the fiber web may be approximatelybetween about 1 and about 99, between about 20 and about 90, or betweenabout 40 and about 70 percent weight of the entire resin formulation ofthe fiber web. Examples of suitable coating methods include generallycompressive techniques such as gravure coating, and size press coating,amongst others; or generally non-compressive techniques in a manner thatminimizes caliper reduction, such as curtain coating, gapped gravurecoating, knife coating, and spray coating, amongst others.

The web and resin formulation mixture is then dried and cured atappropriate conditions. For example, drying and curing times of theresin coating with the fiber may be between about 0.1 seconds and about10 minutes (e.g., about 5 minutes), and temperatures for drying andcuring may be between 100° F. and about 500° F. (e.g., about 300° F.).Once the resin and the fiber web are suitably dried and cured, the fiberweb may be further processed as desired, for example, to form flutes.

In some embodiments, the fiber component(s) may be coated with a numberof resin formulations such that the fiber web has multiple layers ofresin coating or multiple resin formulations in a resin coating. In someembodiments, subsequent resin formulations may be applied to the fibercomponent(s) after a previous resin formulation has been dried. In otherembodiments, subsequent resin formulations may be applied to the fibercomponent(s) during the wet laid process prior to the previous resinformulation being dried. It can be appreciated that multiplecombinations of resin formulations may be used in coating the fiber web(e.g., forming a resin coating gradient and/or forming multiple layersof resin coating) to provide for desired properties of the fiber web.

The flutes may be formed in the fiber web by passing the fiber webthrough male/female corrugation rolls with defined fluting patterns. Insome embodiments, flutes may be formed through deformation and shapesetting through cooling and crosslinking of the fiber web. In somecases, the fluted fiber web may be laminated to another flat media forholding the flutes in place. In some instances, fluting is performed insitu while the resin has not yet fully cured, allowing for flutes toform through the curing process. In some embodiments, fluting occurs asa secondary process after the sheet is constructed and cured. In someembodiments, the fiber web may be heated during fluting. For example,temperatures during fluting of the fiber web may range between about 70°F. and about 500° F.

Application of the resin formulation to the wet laid fiber component(s)using a non-compressive coating technique may provide for a number ofcharacteristics in the fiber web that give rise to increased dustholding capacity. In some instances, non-compressively incorporating theresin with the fibers during the wet phase provides for enhancedstrength of the overall fibrous structure such that the fibrousstructure is less prone to collapse throughout the manufacturingprocess. For example, potential collapse of the fibrous structure mayoccur from applying resin through a compressive gravure/size press. Inlessening the chance for collapse, the fibrous structure may bestrengthened through being partially cured from non-compressiveapplication of the resin in the wet phase and subsequent drying of thefibers. When the strength of the fibrous structure is sufficient toavoid collapse, pore size and/or porosity of the fiber web may bemaintained so as to generally provide enhanced dust holding capacity. Asa result, the fiber web may be manufactured to have both a low thicknessa high dust holding capacity. In having a high dust holding capacity anda low thickness, the fiber webs may be used for a variety ofapplications while generally providing for longer work life of thefilter media.

The fiber webs described herein may be incorporated into a number ofsuitable filter media and filter elements. It should be understood thatthe filter media and filter elements may have a variety of differentconstructions with the particular construction depending on theapplication in which the filter media and elements are used. Forexample, a backing may be applied to a fluted fiber web to form a filtermedia that includes a series of channels between the backing and theweb. In some instances, a low thickness fluted fiber web allows forincorporation of an increased frequency of channels for a given volume.In some cases, more channels provides for increased fluid flow throughthe channels of the fiber web. The assembly may be wrapped to form aspiral arrangement as described further below. In some embodiments, thechannels may be alternately sealed. This configuration allows fluid(e.g., air) to enter through an open channel with the seal(s) directingthe fluid through the web and into an adjacent channel through which ittravels and exits the media. In this respect, fluid includingcontaminants travels in and is filtered through the web. The channelsmay be layered, providing the filter element with a tight, ruggedstructure. In some embodiments, the filter media may be spirally and/orradially wound around a central axis.

FIG. 3 illustrates an embodiment of a filter media that includes afluted fiber web 10 that is laminated to a generally flat backing 30 toform channels 40. The media is in a spiral arrangement. In thisembodiment, the machine direction of the web is in the direction inwhich the web is wound to form the spiral. As shown, fluid is able toreadily flow through the channels. As noted above, alternate channelsmay include seal(s) which direct the fluid into adjacent channels, thus,filtering the fluid. The fluid may exit the channels in a directiondepicted by the dotted lines 50. In some embodiments, the arrangementdepicted in FIG. 3 may be incorporated into a filter element by additionof a housing.

Fiber webs described herein may be formed as multiphase media wheremultiple fiber webs having different (or the same) fiber component(s)may be layered on top of one another. In some embodiments, multiphasefilter media may be formed by placing one fiber dispersion on to anotherfiber dispersion during the wet laid process and subsequently removingthe water from both fiber dispersions. In some cases, a multiphasefilter media (e.g., dual phase) may be tailored to exhibit a suitablegradient in fiber density. Accordingly, dust holding capacity of thefilter media may be increased based on appropriate layering of the fiberwebs.

In addition, fluted fiber webs presented herein may be incorporated intofilter elements for panel, radial, and conical fluid applications. Insome cases, the filter element includes a housing that may be disposedaround the filter media. The housing can have various configurations,with the configurations varying based on the intended application. Insome embodiments, the housing may be formed of a frame that is disposedaround the perimeter of the filter media. For example, the frame may bethermally sealed around the perimeter. In some cases, the frame has agenerally rounded or oval configuration surrounding the element. Theframe may be formed from various materials, including for example,cardboard, metal, polymers, plastic, or any combination of suitablematerials. In some embodiments, the filter element includes an innercore around which the filter media comprising the fiber web is wrapped.Filter media that is radially disposed around an inner core, forexample, in a cylindrical or conical manner, may be suitably supportedby a surrounding frame. The filter elements may also include a varietyof other features known in the art, such as stabilizing features forstabilizing the filter media relative to the frame, spacers, or anyother appropriate feature.

The fiber webs described herein may be incorporated into a number ofsuitable filter elements for use in various applications which make useof their fluted and/or dust holding capacity characteristics. The fiberwebs may be used in applications that take advantage of their toughnessand flexibility which result in a resistance to brittle cracking orfailure. Applications that typically use fiber webs in a flutedconstruction include the construction, agriculture, mining, trucking,and automotive industries. Examples of filter elements that the fiberwebs may be incorporated into include, but are not limited to, radialair filter elements, conical air elements, dust collector cartridges,turbine oil filters, fuel filters, and lube elements, amongst others.

The following non-limiting examples describe fiber webs suitable forflutable applications with high dust holding capacity that have beenmade according to aspects discussed herein.

EXAMPLE 1

A flutable fiber web was produced according to techniques describedabove. The fiber content was 85% weight of the fiber web. Eucalyptushardwood fibers comprised 34% of the fiber web. Pine and spruce softwoodfibers comprised 51% of the fiber web. Of the softwood fibers, 85% byweight were pine and 15% by weight were spruce. The basis weight of thefiber portion of the product was 65 g/m². The resin content made upapproximately 15% by weight of the fiber web and was applied using anon-compressive curtain coater. Vacuum was applied to remove excessresin. Resin and fibers were dried and cured by using steam filleddrying cans. The resin content was comprised of polystyrene acrylatelatex, polyvinyl acetate latex, with a melamine formaldehydecrosslinker. Polystyrene acrylate latex comprised 8.25% by weight of thefiber web and polyvinyl acetate latex comprised 6.3% by weight of thefiber web. Melamine formaldehyde crosslinker comprised 0.5% by weight ofthe fiber web. The Palas filtration performance was measured with PalasModel MFP 2000 coupled with RGB—1000 dust feeder under the operationalconditions as described above for Palas filtration.

EXAMPLE 2

A flutable fiber web was produced similarly to how the fiber web inExample 1 was produced. In this example, the fiber content was 72% byweight of the fiber web. Eucalyptus hardwood fibers comprised 29% byweight of the fiber web. Pine and spruce softwood fibers comprised 43%by weight of the fiber web. The resin content made up 28% by weight ofthe fiber web and was applied using a non-compressive curtain coater.Vacuum was applied to remove excess resin. Resin and fibers were driedand cured by using steam filled drying cans. The resin content wascomprised of polystyrene acrylate latex, polyvinyl acetate latex, with amelamine formaldehyde crosslinker. Polystyrene acrylate latex comprised15.4% by weight of the fiber web and polyvinyl acetate latex comprised11.8% by weight of the fiber web. Melamine formaldehyde comprised 0.8%by weight of the fiber web. The Palas filtration performance wasmeasured with Palas Model MFP 2000 coupled with RGB—1000 dust feederunder the operational conditions as described above for Palasfiltration.

FIG. 4 illustrates a graph of the Palas filtration performance forExamples 1 and 2 with the mass of dust accumulated (mg) shown on thex-axis and pressure drop (Pa) shown on the y-axis. At a pressure drop of1500 Pa, Examples 1 and 2 both exhibit a mass of dust accumulated ofabout 390 mg. The Palas filtration was measured with an area of 100 cm²,providing for a dust holding capacity of 3.9 mg/cm².

Table 1 below provides a summary of the characteristics measured forExamples 1 and 2.

Example 1 Example 2 Weight (g/m²) 76 91 Fiber Content (%) 85 72Hardwood, Eucalyptus (% of fiber web) 34 29 Softwood, pine/spruce (% offiber web) 51 43 Compression during coating no no Resin content (%) 1528 Polystyrene acrylate latex (% of fiber web) 8.25 15.4 Polyvinylacetate latex (% of fiber web) 6.3 11.8 Melamine formaldehyde (% offiber web) 0.5 0.8 Thickness (mils) under 1.5 psi load 14 16 AirPermeability (cfm/sf) at 0.5″ water 36 25 Mean Flow Pore (microns) 17 19Dry Mullen (psi) 27 39 Wet Mullen (psi) 11.4 18 Cured Wet Mullen (psi)11.5 19.3 Wet Mullen Ratio 1.0 0.96 MD Tensile (lb/in) at 2″/min pullrate 19 23 MD Elongation (%) at 2″/min pull rate 4.7 5.2 CD Tensile(lb/in) at 2″/min pull rate 11 15 CD Elongation (%) at 2″/min pull rate7.9 8.0 Tensile Ratio at 2″/min pull rate 1.7 1.5 MD Dry GurleyStiffness (mg) 500 860 MD Wet Gurley Stiffness (mg) 110 180 InitialPalas Pressure Drop (Pa) 180 235 Palas Loading at 1500 Pa (mg of Dust)390 390 Initial Dust Retention (%) 84 88 Palas Efficiency at 0.3 micron68 76 Palas Efficiency at 1.0 micron 64 97

Having thus described several aspects of at least one embodiment of thisinvention, it is to be appreciated various alterations, modifications,and improvements will readily occur to those skilled in the art. Suchalterations, modifications, and improvements are intended to be part ofthis disclosure, and are intended to be within the spirit and scope ofthe invention. Accordingly, the foregoing description and drawings areby way of example only.

What is claimed is:
 1. A fiber web comprising synthetic fibers, whereinthe weight percentage of synthetic fibers is between 50% and 100% of thetotal weight percentage of fibers in the fiber web and the syntheticfibers are wet-laid, the fiber web having: a dust holding capacity ofgreater than about 3 mg/cm² and a thickness of less than about 30 mils.2. The fiber web of claim 1, wherein the fiber web has a dust holdingcapacity of between about 3 mg/cm² and about 8 mg/cm².
 3. The fiber webof claim 2, wherein the weight percentage of synthetic fibers is between50% and 95% of the total weight percentage of fibers in the fiber web 4.The fiber web of claim 1, wherein the weight percentage of syntheticfibers in the fiber web is 100%.
 5. The fiber web of claim 1, whereinthe fiber web has a thickness of between about 5 mils and about 15 mils.6. The fiber web of claim 1, wherein the fiber web includes across-linked resin formulation.
 7. The fiber web of claim 1, wherein thefiber web has a tensile elongation in the cross-machine direction ofgreater than about 2%.
 8. The fiber web of claim 1, wherein the fiberweb has a tensile elongation in the cross-machine direction is betweenabout 2% and about 15%.
 9. The fiber web of claim 1, wherein the fiberweb has a basis weight between 30 g/m² and about 100 g/m².
 10. The fiberweb of claim 1, wherein the fiber web has a permeability of betweenabout 5 cfm/sf and about 200 cfm/sf.
 11. The fiber web of claim 1,wherein the fiber web has a machine direction tensile elongation ofgreater than about 3% and about 8%.
 12. The fiber web of claim 1,wherein the fiber web has a machine direction tensile elongation ofgreater than about 3% and about 5%.
 13. A filter element comprising thefiber web of claim
 1. 14. A fiber web comprising synthetic fibers,wherein the weight percentage of synthetic fibers is between 50% and100% of the total weight percentage of fibers in the fiber web, thefiber web having: a dust holding capacity of greater than about 3mg/cm²; and a basis weight between 30 g/m² and about 100 g/m².
 15. Thefiber web of claim 1, wherein the fiber web has a dust holding capacityof between about 3 mg/cm² and about 8 mg/cm².
 16. The fiber web of claim15, wherein the weight percentage of synthetic fibers is between 50% and95% of the total weight percentage of fibers in the fiber web
 17. Thefiber web of claim 14, wherein the weight percentage of synthetic fibersin the fiber web is 100%.
 18. The fiber web of claim 14, wherein thefiber web has a thickness of between about 5 mils and about 15 mils. 19.The fiber web of claim 14, wherein the fiber web includes a cross-linkedresin formulation.
 20. The fiber web of claim 14, wherein the fiber webhas a tensile elongation in the cross-machine direction of greater thanabout 2%.
 21. The fiber web of claim 14, wherein the fiber web has atensile elongation in the cross-machine direction is between about 2%and about 15%.
 22. The fiber web of claim 14, wherein the fiber web hasa basis weight between 60 g/m² and about 80 g/m².
 23. The fiber web ofclaim 14, wherein the fiber web has a permeability of between about 5cfm/sf and about 200 cfm/sf.
 24. The fiber web of claim 14, wherein thefiber web has a machine direction tensile elongation of greater thanabout 3% and about 8%.
 25. The fiber web of claim 14, wherein the fiberweb has a machine direction tensile elongation of greater than about 3%and about 5%.
 26. The fiber web of claim 14, wherein the syntheticfibers are wet laid.
 27. A filter element comprising the fiber web ofclaim 14.